The evolution of USB standards from 1.1 and 2.0 to 3.x has resulted in changes in appearance, data rates, and cable lengths. Knowing the differences between these standards will help you identify the USB standards of host and peripheral devices and determine their capabilities.
All USB standards can use the same connectors. The color of the plastic inside the connector indicates the USB standard the device or cable is capable of obtaining. USB 1.0 is white, USB 2.0 is black, and USB 3.0 is blue. Connectors with red plastic inside always remain active regardless of the state of the USB connection (for example, active, standby, or sleep) for charging applications.
USB 1.1 was released. It provides data rates from 1.5 Mb to 12 Mb per second, also known as Full Speed.
USB 2.0 increased the supported data rate to 480 Mb per second, also known as High Speed.
The new USB 3.0 standard allowed for data rates up to 5 Gb per second, also known as SuperSpeed.
USB 3.1 increased the supported data rate to 10 Gb per second, also known as SuperSpeed+. USB 3.1 has two variants: USB 3.1 Gen 1 that has a data rate of 5 Gb per second, and USB 3.1 Gen 2 that has a data rate of 10 Gb per second.
The latest USB standard, USB 3.2, has a data rate of 20 Gb per second. With USB 3.2 superseding the older USB 3.x specifications, the USB group came up with a guideline to explain the differences:
The USB 1.1 and USB 2.0 standards are half-duplex, which means they can either send or receive data, but they cannot do both at the same time. The USB 3.x standards support full duplex data transfer, meaning they can send and receive data at the same time.
USB 2.0 devices can reach a maximum cable length of 16’ 5” (5 meters). USB 3.0 devices can reach a maximum cable length of 9’ 10” (3 meters). You can use up to 5 powered hubs to extend USB, but you need to take into account the length parameters of the two different versions of USB and active USB extension cables.
Pinout has also changed with the different USB generations. USB 2.0 only has four copper wires, while USB 3.x models contain nine copper wires.
In late 2019, the USB 4.0 specification was published. This next-generation USB standard is likely to appear in devices in late 2020 or early 2021. Several companies are currently involved in the development of the standard, especially those behind the USB Promoter Group. USB 4.0 builds on the architecture of USB 3.2 and USB 2.0 and is based on the Thunderbolt protocol, recently released by Intel. The standard will double the bandwidth of USB (up to 40 Gb per second) and allow multiple data and screen protocols to be used simultaneously.
Knowing the USB standard supported by your host and peripheral devices will help you set your performance expectations. As with any system, performance is always dictated by the device with the lowest speed and capacity in that system